1. Field of the Invention
The present invention relates to a method for manufacturing thin film transistor to be used for liquid crystal display devices, auto-luminescent display devices and LSIs. In more detail, the present invention relates to a method for manufacturing a thin film transistor by forming a thin film constituting the thin film transistor using a liquid material.
2. Description of Related Art
A thin film transistor is usually composed of thin films such as semiconductor films, insulation films and conductive films. When these thin films are categorized depending on their functions, the insulation films include gate insulation films and interlayer insulation films, and the conductive films are used for gate electrodes, source/drain electrodes, pixel electrodes and wiring lines. These thin films have been mainly deposited by a CVD (Chemical Vapor Deposition) method and a sputtering method.
Silicon films such as amorphous silicon films and poly-silicon films have been mainly used for the semiconductor films. The silicon films have been usually formed by a thermal CVD method, a plasma CVD method or a photo-CVD method using monosilane gas or disilane gas. The thermal CVD method has been generally used for depositing the poly-silicon film (J. Vac. Sci. Technology, vol. 14, p1082 (1977)), while the plasma CVD method has been widely used for depositing the amorphous silicon (Solid State Com., vol. 17, p1193 (1975)).
The silicon film formed by the CVD method have involved some problems to be improved in the manufacturing process: (1) manufacturing yield is low due to contamination of the manufacturing apparatus and generation of foreign substances, since silicon particles appear in the gas phase to be used for the gas phase reaction, (2) a silicon film with a uniform thickness cannot be deposited on a substrate having a rough surface, since a gaseous starting material is used, (3) a step for heating the substrate is required, and productivity is low due to a slow deposition rate of the film, and (4) a complicated and expensive microwave generator and an evacuation apparatus are necessary in the plasma CVD method.
Handling of highly reactive gaseous silicon hydride to be used as a starting material is difficult, besides requiring an air-tight evacuation apparatus as well as a pollutant elimination apparatus for the treatment of exhaust gases. Not only such large scale facility itself is expensive, but also a large amount of energy is consumed in the vacuum system and plasma system, rendering the product a high manufacturing cost.
A method for coating liquid silicon hydride that is free from the vacuum system has been proposed in recent years. Japanese Unexamined Patent Application Publication No. 1-29661 discloses a method for forming a silicon thin film by allowing a gaseous material to be liquefied and absorbed on a chilled substrate as a liquid, followed by allowing the substrate to react with chemically active atomic hydrogen. However, the method also involves a problem that a complicated apparatus is required for continuously evaporating and liquefying silicon hydride, and control of the film thickness is difficult (1).
While Japanese Unexamined Patent Application Publication No.7-267621 discloses a method for coating the substrate with low molecular weight liquid silicon hydride, on the other hand, handling of this complex system is so troublesome that it is difficult to obtain a uniform film thickness when applied to a large area substrate.
While an example of a solid silicon hydride polymer has been reported in UK Patent GB-2077710A, it is impossible to form a film by coating since the compound is insoluble in solvents.
The thermal CVD method, plasma CVD method and sputtering method have been widely used for forming a gate insulation film used for thin film transistors, an insulation film for the interlayer insulation firm, and an electrode conductive film for the gate electrode and source/drain electrodes. The conductive film to be used for the thin film transistor is used for the gate electrode source/drain electrodes wiring lines for connecting among the electrodes, and wiring lines for a power circuit, and a metal film such as Al, Cu, Cr or Ta film is used as the conductive film. The conventional sputtering method is widely used for forming the metal film and siliside film. While a transparent conductive film in addition to the foregoing conductive film is required for the thin film transistor to be used for a liquid crystal display device, an ITO film is usually used for the transparent conductive film, which is deposited by the sputtering method as used in forming the metal film.
The CVD method involves the following four features, which are the same as those in forming the silicon film as an insulation film: (1) manufacturing yield is low due to contamination of the manufacturing apparatus and generation of foreign substances, since silicon particles appear in the gas phase to be used for the gas phase reaction, (2) a silicon film with a uniform thickness can not be deposited on a substrate having a rough surface, since a gaseous starting material is used, (3) a step for heating the substrate is required, and productivity is low due to a slow deposition rate of the film, and (4) a complicated and expensive microwave generator and an evacuation apparatus are necessary in the plasma CVD method.
An evacuation apparatus, in addition to a vacuum pump as well as a target material, a sputtering power source and a substrate heating apparatus, are required for the sputtering method to be utilized in forming the conductive film mainly comprising a metal film and the transparent conductive film. Although a toxic and combustible gas is seldom used in the sputtering method as compared with the CVD method, the film is deposited not only on the substrate as a film deposition object but also on the inner wall of the chamber in which the substrate is placed. Peeled pieces of the deposition material from the inner wall serve as foreign substances during the film deposition process to result in decreased manufacturing yield of the product as in the CVD method. It is the common drawbacks of the sputtering method with the CVD method that the film thickness is uneven at the rough portions on the surface of the substrate, productivity is low, and the facilities become large scale and expensive because an evacuation apparatus is required.
The method for forming the thin film by the conventional CVD method and sputtering method have involved the problems of low productivity, high incidence of film defects and low yield, uneven film thickness at the rough surface portions, and breakage of wiring patterns at the steps. These problems also cause increased manufacturing cost of the thin film transistor. These problems in the CVD method and sputtering method arise from intrinsic features of the film deposition method such as use of the evacuation apparatus, need of heating of the substrate, requirement of a power source for plasma generation, and film deposition on unnecessary portions such as the inner wall of the apparatus other than the substrate. These intrinsic features arise other problems that the large scale apparatus leads to a high facility cost, and the running cost of the apparatus is also high.
The present invention proposes a method for manufacturing a thin film transistor by a novel method essentially different from the conventional film deposition method. While the thin films such as a silicon film and an insulation film in the thin film transistor have been deposited by a CVD method or a sputtering method, a desired thin film is formed in the present invention by coating a substrate with a liquid material to form a coating film, followed by heat-treating the coating film.
The object of the present invention is to provide a method for solving the intrinsic problems involved in the conventional film deposition method, providing a method for manufacturing a thin film transistor with a low manufacturing cost using a compact and cheap apparatus for forming a thin film with high productivity, less incidence of film defects, high manufacturing yield, small number of wiring breakage at the steps, and low manufacturing cost.
All or a part of the thin films such as the silicon film, insulation film and conductive film constituting the thin film transistor are formed using a liquid material in the present invention for solving the foregoing problems. The method mainly comprises the steps of: forming a coating film by coating a substrate with the liquid material; and forming a desired thin film by heat-treating the coating film.
In a first aspect of the method for manufacturing a thin film transistor, the silicon film is formed by the steps comprising: forming a coating film by coating a liquid material containing silicon atoms; and heat-treating and/or irradiating a light for converting the coating film into the silicon film.
In the first aspect so configured as described above, the heat treatment step desirably comprises a first heat-treatment step for converting the coated liquid material into an amorphous silicon film, and a second heat treatment step for converting the amorphous silicon film into a polycrystalline silicon film.
Preferably, the liquid material containing silicon atoms contains a silicon compound having a cyclic group represented by a general formula of SinXm (wherein n represents an integer of 5 or more, m represents an integer of n, 2nxe2x88x922 or 2n, and X represents a hydrogen atom and/or a halogen atom) in the first aspect described above.
It is desirable that n is an integer in the range of 5 or more and 20 or less in the silicon compound having a cyclic group represented by the general formula of SinXm in the silicon compound having a cyclic group represented by a general formula of SinXm (wherein n represents an integer of 5 or more, m represents an integer of n, 2nxe2x88x922 or 2n, and X represents a hydrogen atom and/or a halogen atom) in the first aspect described above.
It is also desirable that the solute concentration of the solution containing the silicon compound having a cyclic group represented by the general formula of SinXm is in the range of 1 to 80% by weight.
It is also desirable that the solution containing the silicon compound having a cyclic group represented by the general formula of SinXm has a viscosity of 1 to 100 mPaxc2x7s.
It is also desirable that the solution containing the silicon compound having a cyclic group represented by the general formula of SinXm has a vapor pressure of 0.001 to 100 mgHg at room temperature.
It is also desirable that hydrocarbons are used for the solvent for the solution containing the silicon compound having a cyclic group represented by the general formula of SinXm.
In a second aspect, the present invention provides a method for manufacturing a thin film transistor formed on an insulation substrate or insulation film, comprising the steps of: forming a coating film by coating a liquid material containing silicon atoms; and heat-treating for converting the coating film into the silicon film, the step for forming the gate insulation film and interlayer insulation film comprising the steps of coating the substrate with polysilazane, and converting coated polysilazane into an SiO2 film by heat-treatment.
In a third aspect, the present invention provides a method for manufacturing a thin film transistor formed on an insulation substrate or insulation film, comprising the steps of: forming a coating film by coating a liquid material containing silicon atoms on the substrate; and heat-treating for converting the coating film into a silicon film, the step for forming the a gate electrode and source/drain electrode comprising forming a coating film by coating a liquid material containing a metal on the substrate, converting the coating film into a conductive film by heat-treatment, and patterning the conductive film.
It is preferable in the third aspect that the gate electrode and the source/drain electrodes are formed by forming a conductive film on the substrate by plating, followed by patterning the conductive film.
It is preferable in the third aspect that the gate electrode and source/drain electrodes are formed by the steps comprising: forming a conductive film on the substrate by plating; and patterning the conductive film.
It is preferable in the third aspect that the gate electrode and source/drain electrode are formed by the steps comprising: forming a coating film by coating an organic compound containing indium and tin; and heat-treating for converting the coating film into an ITO (Indium-Tin-Oxide) film.
In a fourth aspect, the present invention provides a method for manufacturing a thin film transistor formed on an insulation substrate or insulation film, comprising the steps of: forming a coating film by coating a liquid material containing silicon atoms on the substrate; heat-treating for converting the coating film into a silicon film, the step for forming a transparent conductive film comprising forming a coating film by coating an organic compound containing indium and tin; and heat-treating for converting the coating film into an ITO (Indium-Tin-Oxide) film.
In a fifth aspect, the present invention provides a method for manufacturing a thin film transistor formed on an insulation substrate or insulation film, comprising the steps of: forming a coating film by coating a liquid material containing silicon atoms on an insulation substrate or insulation film; heat-treating for converting the coating film into a silicon film; forming an islet region that serves as a source, drain and channel by pattering the silicon film; forming a gate insulation film; forming a gate electrode; injecting impurities into the source/drain regions; forming an interlayer insulation film; opening contact holes on the interlayer insulation film; and forming electrodes and wiring lines.
In a sixth aspect, the present invention provides a method for manufacturing a thin film transistor formed on an insulation substrate or insulation film, comprising the steps of: forming a semiconductor layer that serves as a source/drain regions on am insulation substrate or insulation film; forming a coating film by coating a liquid material containing silicon atoms on the substrate; heat-treating for converting the coating film into a silicon film; forming an islet region that serves as a channel region to be connected to the source/drain regions by patterning the silicon film; forming a gate insulation layer; forming a gate electrode; forming an interlayer insulation film; opening contact holes on the interlayer insulation film; and forming electrodes and wiring lines.
In a seventh aspect, the present invention provides a method for manufacturing a thin film transistor formed on an insulation substrate or insulation film, comprising the steps of forming a gate electrode on an insulation substrate or insulation film; forming a gate insulation layer; forming a coating film by coating a liquid material containing silicon atoms on the substrate; heat-treating for converting the coating film into a silicon film; forming a semiconductor layer that serves as source/drain regions; and forming electrodes and wiring lines.
In a eighth aspect, the present invention provides a method for manufacturing a thin film transistor comprising thin films of a silicon film, an insulation film and a conductive film, wherein all the thin films are formed using a liquid material, and the method for forming the thin films comprises no evacuation apparatus.
In a different aspect, the present invention provides a method for manufacturing a thin film transistor comprising thin films of a silicon film, a gate insulation film, a gate electrode conductive film, an interlayer insulation film, a conductive film for electrodes and wiring lines, and a transparent conductive film, wherein all the thin films are formed using a liquid material, and the method for forming the thin films comprises no evacuation apparatus.